Automation, cutting upgrades set to slash reactor removal costs
Deployment of arc saws, underwater lasers and self-operating systems could shorten reactor segmentation projects and cut costs, Richard Reid, Technical Executive, EPRI Decommissioning Technology Program, told the Fourth Annual Nuclear Decommissioning & Used Fuel Strategy Summit.
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Rising decommissioning activity has prompted the development of new technologies and business models which shorten project durations and control costs. Last year, the U.S. Electric Power Research Institute (EPRI) launched a research project to evaluate advanced techniques for segmentation of reactor internals in a bid to improve efficiency and safety.
EPRI evaluated 26 mechanical and 23 thermal cutting techniques as well as over 20 manipulation and support systems used for the cutting process and the handling of segmented material. The study compared the benefits of the different technologies and identified current gaps and potential improvements.
Reactor internal segmentation is one of the most complex decommissioning tasks, requiring years of planning and a year or longer to execute. Plant operators look to minimize the duration of fuel transfer and reactor dismantling projects due to the high labor costs associated with monitoring and handling spent fuel and radioactive components.
Conventional reactor cutting tools can be relatively slow and generate unhelpful gases and fine materials which can degrade water clarity and increase worker exposure. Secondary waste materials can increase waste volume and waste handling, packaging and transport costs.
"What we want to do is develop an integrated system for reactor internal segmentation with a goal to make this project more predictable, faster, safer and more cost-effective," Reid told the Summit on October 2.
Operators would benefit from more accurate and rigid manipulation equipment to control cutting activities and improvements in the equipment used to manipulate segmented components, he said.
Greater use of automation would also improve the efficiency of the manipulation processes, Reid said.
"Let's use the technology that's developed and used in other industries - start using them more in the decommissioning arena. That's one of the things EPRI is really focusing on," he said.
Cutting times
Arc saw technology has been around for several decades but has not been used for commercial reactor internal segmentation. Barriers to use have included the heavy weight of the machinery and debris generation, but the technology has several advantages, including a cutting speed reported to be 40 times faster than plasma cutting.
EPRI is currently working with the Department of Energy (DOE) to demonstrate some of the advantages of using Arc saw technology for reactor internal segmentation, Reid said.
"In terms of capability it has some very good advantages...It's not been used currently, we think maybe it should be," he said.
Arc saws use an electrical discharge which means the disc does not contact the metal being cut, Reid noted.
"You have a very long blade life with this technology and a very robust cut, you can cut through 20 inches of metal," he said.
In addition, arc saws do not use compressed gas and therefore do not require gas collection methods, and they generate minimal quantities of gas.
Precision work
Greater cutting accuracy allows operators to segment reactor pieces in shapes and weights which optimize loading into storage canisters.
A number of research groups in the U.S., UK and France are developing underwater laser cutting technology for use in commercial nuclear projects.
Underwater laser cutting provides a fast, compact, lightweight and reliable cutting method for segmentation of reactor internals, Reid said.
"One of the advantages of laser cutting is you get a very narrow and very precise cut. It's another promising technology we would like to see developed to see if it does have a good application for internal segmentation," he said.
Disadvantages with laser cutting include the generation of fine materials which can create water quality issues and this will require collection and filtration methods, Reid said.
Laser cutting also requires the use of gas and therefore will require appropriate control processes for the dispersal of radioactive material.
Autonomous control
Another way in which operators can increase efficiency is using semi-autonomous operations through a combination of 3-D virtual models, sensors, data processing and remotely controlled equipment.
Data processing can steer recommended cutting paths and be integrated with inverse kinematics to control robotic movements. Operators can intervene if parameters are exceeded.
One of the important elements to using semi-autonomous operations is to have an efficient feedback system to the operating system, Reid said.
"The technology to have this feedback loop already exist - it's used in many other industries... You can have a vision system, such as a LIDAR system which is a very mature technology, feed that back to the equipment," he said.
EPRI has completed its evaluation of different technologies and is now developing a conceptual design for a coordinated semi-autonomous system, Reid said.
In 2018-2019, EPRI hopes to work with industrial partners to manufacture, test and demonstrate the integrated system generates efficiency improvements, he said.
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